linux-kernel - Re: [PATCH] x86/PCI: Use MMCONFIG by default for KVM guests

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Message-ID: <20200722025912.GM15516@casper.infradead.org>
Date:   Wed, 22 Jul 2020 03:59:12 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Julia Suvorova <jusual@...hat.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH] x86/PCI: Use MMCONFIG by default for KVM guests

On Wed, Jul 22, 2020 at 02:15:13AM +0200, Julia Suvorova wrote:
> @@ -264,6 +265,10 @@ void __init pci_direct_init(int type)
>  {
>  	if (type == 0)
>  		return;
> +
> +	if (raw_pci_ext_ops && kvm_para_available())
> +		return;

This is a bit of a subtle way of saying "If mmconfig exists, don't use
the cf8 mechanism".  There's probably a better way of doing this, but
the x86 pci init sequence is already byzantine and I don't understand it
well enough to offer you an alternative.